The present invention relates to an infusion pump for controlled delivery of a pharmaceutical product to a subject, and more specifically to an infusion pump having a sealed drive mechanism and improved method of occlusion detection for determining the presence of obstructions in the infusion path.
Infusion pumps provide a significant lifestyle benefit for individuals requiring multiple deliveries of volumetrically proportioned medication to their body over a period of time. Infusion pumps reliably dispense the required medication to the patient through an infusion path established between the patient and the pump. The infusion path is a conduit secured to the pump at one end and secured intravenously or subcutaneously to a patient on the other. The operation of the infusion pump is controlled by a processor. The processor controls the delivery of periodic dosages of medication to a patient at predetermined times. Thus, a patient is able to rely on the infusion pump for delivering the required dosage of medication intravenously or subcutaneously over a period of time. In this way, the patient need not interrupt life activities for repeated manual delivery of required medication.
As is known, infusion pumps often employ a piston-type drive mechanism for urging the contents of a pharmaceutical cartridge or xe2x80x9csyringexe2x80x9d internal to the pump along the infusion path to the subject. Piston-type infusion pumps are susceptible to an occlusion in the infusion path. Additionally, piston-type infusion pumps include complicated drive assemblies which require periodic maintenance and/or user adjustment which further degrades the reliability of the device.
Most piston-type infusion pumps have an exposed lead-screw drive assembly that is manipulated by the user to reset the device each time a new syringe is inserted in the device. Because the lead screw is a precision mechanical assembly that drives a plunger through the syringe to infuse pharmaceutical product along an infusion path, dirt and debris in the exposed lead screw can cause the screw thread to either wear-down or lock-up at its point of engagement with a mated drive, either of which can cause a pump failure. Some manufacturers suggest periodic cleaning of the lead screw, while the other manufacturers have equipped their devices with disposable lead screws and nut assemblies to prevent such malfunctions. Installation of these parts in some pumps requires partial disassembly of the device, further complicating syringe installation. Furthermore, many piston type infusion pumps are used with syringe plungers manufactured with xe2x80x9cOxe2x80x9d-rings. The installation of the syringe will often break the plunger seal about the O-ring and cause medication to leak through the plunger into the pump, possibly damaging electrical components, but also causing medication not being delivered properly to the patients through infusion set electronics. Moreover, there is a need for an infusion pump with sealed and inaccessible electronics so the pump does not become damaged due to accidental or deliberate submersion in water, and a sealed drive mechanism to prevent damage to the lead screw.
Often piston-type infusion pumps also do not show the amount of medication remaining in a syringe. Some manufacturers use a transparent window to visually inspect whether a syringe requires replacement. If a patient is not diligent about making such visual checks, he runs the risk of running out of medication. Other pumps indirectly determine the amount of remaining medication and, therefore, are subject to inaccuracies. Thus, there is a need for an infusion pump that directly reports the amount of remaining medication.
While some infusion pumps are designed to subtract delivery volumes from a fixed full or a fixed half syringe volume, the amount of medication in the syringe must be manually entered into the device at the outset by the patient upon installation of the syringe, although it may actually be neither full nor half full initially. This requirement is still a further complication of the syringe installation process.
Regarding occlusion detection, when an occlusion occurs anywhere along the infusion path of a piston-type pump, medication is not delivered to the patient even though the piston moves to deliver the medication. As can be appreciated, the existence of an occlusion will prevent the infusion pump from delivering medication to a patient until the occlusion is detected and cleared from the infusion path. Thus, the rapid detection of occlusions along the infusion path is key to reliable operation of a pump.
Presently, a piston-type infusion pump is desired which provides an improved method of occlusion detection, the pump including a simplified and reliable piston-type drive mechanism.
The present invention is directed to a piston-type infusion pump which includes an enclosed lead screw which can not be accessed without disassembling the pump. Thus, the engagement and disengagement of drive mechanism are achieved remotely, by latching and unlatching of the pump door, minimizing likely user error or abuse. The pharmaceutical syringe has a U-shaped plunger designed to link with the drive mechanism for simple installation. Additionally, the pump displays exact amount of medication (i.e., insulin) remaining in the cartridge at any time and utilizes an improved method of occlusion detection.
Briefly stated, the present invention provides a piston-type infusion pump having a remotely engaged piston-type drive mechanism and improved method of occlusion detection. The internal components of the pump are sealed from the outside when a pharmaceutical syringe is installed, thus creating a watertight seal when the pump is in its operational mode.
The infusion pump is designed to remotely engage and disengage the lead screw of a drive mechanism by way of a latch stem, which is a part of a pump door latching mechanism. The pump door latch has a watertight rotary seal between the casing of the infusion pump and the latch stem. When the pump door latch is moved up to allow the pump door to open, it disengages the drive, so that the plunger of the syringe is free to move. When the pump door latch is pushed down to lock the pump door of the infusion pump, it engages the drive. When in the locked position the plunger is moved only through rotation of the lead screw. Thus, the engagement and disengagement of drive mechanism are achieved remotely, by latching and unlatching of the pump door, minimizing likely user error or abuse.
The infusion pump includes processing circuitry for controlling the drive mechanism to infuse medication to a patient, including a sensor to track the position of the syringe plunger. The sensor provides information that determines the volume of remaining insulin at any time in the pump. The infusion pump processing circuitry also includes a force sensor and circuitry for uniquely processing signals indicative of the presence of an occlusion along the infusion path. The occlusion detector operates with good accuracy at low volumes and delivery rates.